How to best handle a one direction sync chain?

[ell1e (Ellie)]

I have a friend with device A, for whom I store a copy of a folder via syncthing for redundancy on device B. Since it’s ultimately my friend’s folder I don’t want to accidentally change it, so I would want syncthing not to write anything in that direction. However, for additional redundancy I have device C, and I want everything to also be synced from B to C, just in case.

This would mean I want changes to flow in this direction A –> B –> C but never in the other direction.

Is this somehow possible to do? It seems like when I make the folder send only on device B, it won’t be able to send it to C anymore. I have been wondering what exactly I best do here to solve that.

Any suggestions appreciated! Ideally something that requires no changes on device A, since my friend isn’t very techie so I don’t want to bother them with understanding what I’m even doing on my end.

[marbens (Marcus B Spencer)]

I think you want the folders to be set as Receive Only on devices B and C.

It is smart enough to tell the difference between local and remote changes.

Excerpt from Folder Types — Syncthing documentation (emphasis mine):

The receive only folder is the logical opposite of the send only folder. In this mode, all changes from the cluster are applied and redistributed to other devices, as they are in the default send-receive mode. Local changes are however not distributed to other devices.

[ell1e (Ellie)]

Ohhh I didn’t realize that! Thank you so much, I didn’t expect it to be so easy.